Add 5 cups ice, 1 packet orange Kool-Aid, 1/2 cup granulated sugar, 1 cup orange juice, 1/2 cup Cointreau, and 1/2 cup vodka to a blender.
Cover and blend until thick, icy, and spoonable.
Pour into wine glasses and garnish with orange slices and mint sprigs. Serve immediately.
Notes
Make Ahead: Blend the slush and transfer it to a freezer-safe container. Freeze until ready to serve. Let it sit at room temperature for a few minutes before stirring and serving.
Sweetness Tip: Reduce the sugar slightly for a less-sweet slush.
Freezing Tip: Avoid adding extra vodka if freezing the mixture, as additional alcohol can keep it from setting properly.